Direct fuel injection has some distinct advantages over prior art systems with respect to emissions and fuel economy of an engine of a vehicle. This is mainly because of an increase in the efficiency of the engine.
Direct fuel injection systems may include a common rail which supplies individual injectors with fuel. The common rail is, in turn, supplied by a pump that generates a relatively high pressure, e.g., 2000 bar. One such pump is shown in U.S. patent application Ser. No. 09/031,859, filed Feb. 27, 1998, and entitled "Supply Pump For Gasoline Common Rail", which is assigned to the present assignee hereof.
For safety considerations, the common rail may be equipped with a pressure relief valve which functions to reduce pressure and, for example, return fuel to a fuel tank in the event that the pressure level in the common rail becomes excessive. In particular, where the pressure of the fluid within the common rail rises above a threshold pressure, fluid must be released in order to prevent a critical rupture.
It is also been found that once pressure within the common rail has risen above the threshold, continuous regulation of the fluid pressure is desirable to continue operation of the vehicle.